Significance Substantial data derived both from human studies and from studies of nonhuman primates indicates that face perception is a specialized brain function. While a network of brain regions is involved in this function, the amygdala appears to be specifically involved in the interpretation of social signals, including expressions, conveyed by the face. Understanding the neural systems that enable the interpretation of facial expressions will provide important insight into normal social communication and will contribute evidence concerning the pathophysiology of neurodevelopmental disorders of social perception such as autism. Objectives Large numbers (50-200) of individual neurons will be recorded from the amygdala of macaque monkeys while the subject animals are viewing video images of monkey faces. We will determine the ensemble code that the amygdala produces for different facial expressions. We will also determine how the code is modified depending on the social context of the animal. Neurons will be recorded simultaneously from at least three of the major subdivisions of the amygdala. Results Feasibility studies have been carried out in four macaque monkeys. Successful recordings have been made from up to 40 neurons using prototype multielectrode arrays designed for the monkey brain. A laboratory designed for state-of-the-art parallel unit recording in the awake behaving monkey is now under construction. Stimuli have been produced and the CORTEX stimulus presentation and data acquisition system has been set up at the laboratory. Further progress must await additional extramural funding. A Silvio O Conte Feasibility Center application has been submitted to the NIMH and will be reviewed during the March/April 1999 period. Future Directions Once extramural funding is established, experiments will be initiated to examine neuronal responses in the monkey amygdala to the identity of monkey faces and to monkey facial expressions throughout the full extent of the lateral and basal nuclei. We will then determine how these responses are modified by relevant social knowledge about the stimulus monkeys. The hypothesized functions of the nuclei of he amygdala are based on our long standing neuroanatomical studies of this region. KEY WORDS amygdala, facial expression, neurons, electrophysiology FUNDING Pending NIMH Proposal